The present invention relates to a method of and to an apparatus for the making of a continuous tobacco stream. More particularly, the invention relates to improvements in a method of and in an apparatus for the making of a tobacco stream which contains different types of tobacco. Still more particularly, the invention relates to improvements in a method of and in an apparatus for the making of a composite tobacco stream wherein a core consisting of or containing a first type of tobacco is surrounded by a tubular envelope or shell consisting of or containing a second type of tobacco.
It is already known to form a tobacco stream wherein a core containing tobacco particles of a first type is confined in a tubular envelope consisting of tobacco particles of a second type. In accordance with heretofore known proposals, such tobacco stream is obtained by showering a first tobacco layer onto the exposed side of an air-permeable conveyor the other side of which is adjacent to a suction chamber so that the pressure differential suffices to attract the first layer to the exposed side of the conveyor. The conveyor constitutes the mobile bottom wall of an elongated tobacco channel which further includes two sidewalls and has a substantially square or rectangular cross-sectional outline. In the next step, a relatively narrow second tobacco layer (consisting of a material other than the material of the first layer) is showered onto the first layer so that the marginal portions of the first layer extend laterally beyond the second layer. In a further step, the channel receives a third tobacco layer whose material is identical with that of the first layer and which overlies the second layer as well as the marginal portions of the first layer. The first and third layers form an envelope for the second layer. Reference may be had, for example, to German Offenlegungsschrift No. 20 15 387 and to German Pat. No. 22 46 976. The Offenlegungsschrift discloses an apparatus wherein the first tobacco layer is originally flat and is thereupon deformed by appropriate shaping of the path for the air-permeable conveyor so that the thus deformed first layer exhibits an exposed concave surface and constitutes a substantially trough- or gutter-shaped receptacle for the narrower second layer. The conversion of the originally flat first tobacco layer into a gutter-shaped layer is assisted by a needle-like shaping tool which engages the exposed side of the first layer during deformation of the conveyor. The introductory part of the aforementioned German patent discloses that such conversion of an originally flat tobacco layer into a concavo-convex layer presents or is likely to present problems and, in order to eliminate such problems, the German patent proposes to install in the tobacco channel a partition which divides the mass of showered tobacco particles and is spaced apart from the exposed side of the conveyor by a distance corresponding to the desired thickness of the central longitudinal portion of the first tobacco layer, namely, of that portion which is to be overlapped by the second tobacco layer. The purpose of the partition is to prevent the penetration of tobacco particles, which are to form the first layer, into that zone of the channel which is about to receive the particles constituting the second layer. A drawback of such proposal is that the partition increases the likelihood of clogging of the tobacco channel.